These studies were conducted to determine the species-specific and differentiation stage-specific nature of three activities of inflammatory cells: proliferation, disulfide-cleaving capacity and expression of gamma-glutamyltranspeptidase (gGTP). Earlier studies indicated that the latter two activities create a reducing (antioxidative) environment around the cells, thereby being permissive of the proliferation. Multiple monocyte/macrophage/myeloid cell lines of either human or murine origin were cultured under various specified conditions so that direct comparisons under identical conditions could be made. The question of influence of differentiation state was only partially answered by the selected array of cell lines; more-differentiated cells proliferate less vigorously; disulfide-cleaving activity and gGTP expression were, in all cases proportional to proliferation as with the more rapidly dividing cells. The species differences (and, thereby, the applicability to human use) were quite clearly defined: 1) for proliferation, cells of equal differentiation state were equal, irrespective of species; 2) human gGTP was greater than the murine gGTP; and 3) human disulfide-cleaving activity was greater or equal to the murine activity. These findings further contribute to the utility of manipulation of these cell activities in the potential control of inflammatory cell activities.